Intermolecular forces correlation equations

Solvent effects are due to intermolecular forces. A number of different correlation equations have been proposed for modeling the effect of varying solvent on chemical... 

The modulus of elasticity in the glassy state depends on intermolecular forces 1 (. Therefore, Tobolsky 28) proposed the following equation correlating the bulk modulus of elasticity (B) at 0 K and cohesive energy density (82) ... 

Modern theoretical developments in the molecular thermodynamics of liquid-solution behavior are based on the concept of local composition. Within a liquid solution, local compositions, different from the overall mixture composition, are presumed to account for the short-range order and nonrandom molecular orientations that result from differences in molecular size and intermolecular forces. The concept was introduced by G. M. Wilson in 1964 with the publication of a model of solution behavior since known as the Wilson equation. The success of this equation in the correlation of VLE data prompted the development of alternative local-composition models, most notably the NRTL (Non-Random-Two Liquid) equation of Renon and Prausnitz and the UNIQUAC (UNIversal QUAsi-Chemical) equation of Abrams and Prausnitz. A further significant development, based on the UNIQUAC equation, is the UNIFAC method,tt in which activity coefficients are calculated from contributions of the various groups making up the molecules of a solution. 

We propose the study of Lennard-Jones (LJ) mixtures that simulate the carbon dioxide-naphthalene system. The LJ fluid is used only as a model, as real CO2 and CioHg are far from LJ particles. The rationale is that supercritical solubility enhancement is common to all fluids exhibiting critical behavior, irrespective of their specific intermolecular forces. Study of simpler models will bring out the salient features without the complications of details. The accurate HMSA integral equation (Ifl) is employed to calculate the pair correlation functions at various conditions characteristic of supercritical solutions. In closely related work reported elsewhere (Pfund, D. M. Lee, L. L. Cochran, H. D. Int. J. Thermophvs. in press and Fluid Phase Equilib. in preparation) we have explored methods of determining chemical potentials in solutions from molecular distribution functions. 

One notable feature of this work, and of all the polymers so far investigated, is the excellent correlation of the results with the linear relation predicted by Equation 3 despite the obvious approximations underlying the method and the various types of polymer studied. This has inevitably prompted further speculation and comment. A particularly intriguing aspect is that the same results have been obtained irrespective of the polarity of the polymer and solvents so that the nature of the intermolecular forces in the solution appear to have little effect [32]. 

A Review of Correlations for ky. Justification for using the geometric mean for ey—and for Tcij—is provided by London s theory of dispersion forces. When Londons expression for the intermolecular energy is equated to the attractive part of the Lennard-Jones (LJ) 12 6 potential, the following relationship obtains ... 

Charton s intermolecular force equation (IMF) is the best model covering all physicochemical and physicobiochemical events (97), but it is not in general use. Hansch (98), Fujita (99) and Verloop (100) all use internally consistent variations in their own research. By any consistent approach, accidental correlations are of little concern in the analysis of statistically large (n>30) sets of well measured binding data. Even smaller sets can reliably extract the major mechanistic components provided overdescription is not attempted (less than 4 data points/variable). 

Another problem with the interpretation of multiparameter equations such as [ 13.1.2] arises since some of the parameters used are not fully independent of one another. As to this, the trend between jf and a has already been mentioned. Similarly, the parameter displays some connection to the polarity indices. Virtually, the various parameters feature just different blends of more fundamental intermolecular forces (see below). Because of this, the interpretations of empirical solvent-reactivity correlations are often based more on intuition or preconceived opinion than on physically defined interaction mechanisms. As it... 

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